1. Field of the Invention
The present invention relates to water quality testing methods, and particularly to a method for detection of cyanide in water, to an electrode used in the method that has a coating of a thin film of ZnO2 nanoparticles thereon, and to a method of forming ZnO2 nanoparticles by laser ablation.
2. Description of the Related Art
Cyanide is used in many industrial applications, such as electroplating, precious metal refining, metal mining, metal ore processing, smelting, and other chemical and petrochemical applications.
Exposure to cyanide ions can occur through inhalation, ingestion, eye or skin contact, and absorption through the skin, eyes, and mucous membranes. It can cause rapid death due to metabolic asphyxiation. Cyanide is extremely toxic, and even relatively small amounts of this species are lethal to humans. The toxicity of cyanide results from its propensity to bind the iron in cytochrome c oxidase, interfering with electron transport and resulting in hypoxia. Death can occur within seconds or minutes of the inhalation of high concentrations of hydrogen cyanide gas. A recent study reports that 270 ppm is fatal after 6 to 8 minutes, 181 ppm after 10 minutes and 135 ppm after 30 minutes. Cyanide directly stimulates the chemoreceptor of the carotid and aortic bodies, causing hyperpnea. Cardiac irregularities are often noted. Industrial exposure to hydrogen cyanide solutions has caused dermatitis, itching, scarlet rash, papules, and nose irritation and bleeding. Perforation of the nasal septum has also occurred.
Thus, there exists a need for an efficient sensing system for cyanide to monitor cyanide concentration from contaminant sources.
The Environmental Protection Agency (EPA) has set the maximum contaminant level (MCL) for cyanide as free cyanide (which includes both hydrogen cyanide [HCN] and CN− ions) at 0.2 mg/L to regulate the safe levels for drinking water. Different methods have been reported in literature for free cyanide detection, including amenable cyanide (Standard Methods SM-4500-G) [8] with either titration SM-4500-D), colorimetric SM-4500-E), or ion selective electrode (ISE) (SM4500-CN-F) detection methods, and free cyanide detected directly by an ISE. Other methods in current use for determination of cyanide include titration, colorimetric, ion selective electrode, ion chromatography methods and Raman and IR spectroscopy. However, each of these methods has one or more problems associated therewith.
Using laser to ablate materials has been applied in laser-based materials processing for many years. Recently, two popular methods have been developed in nanomaterials preparations: pulsed laser ablation deposition (PLAD) to prepare thin films, and pulsed laser ablation (PLA) to produce nanoparticles, nanorods and nanotubes in liquids. PLA of solid target in a liquid medium has been used for preparing metal, metal oxide, and alloy nanoparticles. However, most of these processes rely on ablation onto solid target that produce not very high yield.
Metal oxide nanoparticles provide a favorable conducive environment for molecules to transfer electrons with underlying electrodes because of the structure stability and small size of inorganic nanoparticles, which provide a larger surface area than plating. Moreover, the small pores in metal oxide could act as a substrate containing transport channels to decrease mass transfer resistance for efficient mobility of charged species, which could enhance the sensitivity of an electrode.
Thus, a method for detection of cyanide in water solving the aforementioned problems is desired.